The original IBM PC didn't have a keyboard controller. Many things changed when the second generation PC's came out, the IBM AT with it's 286 CPU introduced the keyboard controller and that was IBM's hack for switching from protected to real mode. Communication between the keyboard itself and the computer also changed. Before the AT/286 there wasn't any possibility for the computer to control keyboard LED's. Some third party 100+ key keyboards for PC/XT/8088's had problems with loosing track of numlock state sometimes, ending up with the cursor keys and pgup/pgdn/end/home/delete/insert always sending numerical keypad numbers no matter what state numlock was in... If you find an old keyboard there is a good chance it has a "XT/AT" switch somewhere...
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original IBM PC...
Date: 2011-06-11 01:13 pm (UTC)The original IBM PC didn't have a keyboard controller.
Many things changed when the second generation PC's came out, the IBM AT with it's 286 CPU introduced the keyboard controller and that was IBM's hack for switching from protected to real mode. Communication between the keyboard itself and the computer also changed. Before the AT/286 there wasn't any possibility for the computer to control keyboard LED's. Some third party 100+ key keyboards for PC/XT/8088's had problems with loosing track of numlock state sometimes, ending up with the cursor keys and pgup/pgdn/end/home/delete/insert always sending numerical keypad numbers no matter what state numlock was in...
If you find an old keyboard there is a good chance it has a "XT/AT" switch somewhere...